The present invention relates to an IC card-type modem which executes a data communication between a terminal equipment and a switch through a telephone line by modulating and demodulating data stored in the terminal equipment, and relates to a method for communicating data by the IC card-type modem.
The data communication has been executed by the modem equipment (a modulator demodulator) up to the present. The modem equipment modulates digital data transmitted from a personal computer into an analog data, and transmits the analog data to the telephone line. Also, the modem equipment demodulates the analog data transmitted from the telephone line into digital data, and transmits the digital data to the personal computer.
Recently, circuit parts have been accommodated within the IC (Integrated Circuit) card so as to plan a miniaturization of the modem equipment. The construction which is in conformity with standards of Japan Electronic Industry Development Association (JEIDA) or Personal Computer Memory Card International Association (PCMCIA) is adopted in the IC card-type modem.
For instance, the size of the IC card-type modem which is in conformity with the standard of JEIDA is 54 mm in width, 85.6 mm in length and 5 mm in thickness. Further, the size of the IC card-type modem is almost the same as the size of the IC card-type modem which is in conformity with the standard of PCMCIA.
However, a height of such large-sized parts as a line transformer connected to the telephone line is more than 5 mm. For this reason, the large-sized parts did not meet the standards. In this case, the line transformer could not be mounted within the IC card, so the line transformer was installed outside of the IC card. However, a charm of the product is deteriorated when the parts are installed outside of the IC card. Accordingly, a small-sized and sheet-type line transformer has been mounted within the IC card by methods of every kind up to the present.
For instance, an effect that the whole modem is thinned to be accommodated in the IC card is mentioned in 268379 number of Patent Disclosure in 1993 which has been already well-known. Besides, the effect that a DC loop-circuit and the line transformer are integrated is mentioned in 327791 number of Patent Disclosure in 1993 and in 268372 number of Patent disclosure in 1993. The DC loop circuit and the line transformer are integrated by a pseudo inductance circuit comprising a transistor, a resistor and a capacitor, and a coupling capacitor.
However, a small-sized and sheet-type line transformer mounted on the IC card could not meet the line standards of each nationality. Namely, the line standard of each nationality is specified in accordance with such actual circumstances as a line impedance in each nationality. Hereupon, one card-type modem can correspond to the standards of each nationality if there is some space in a design margin of the IC card-type modem, when the difference of standard value per nationality is small within each term of the line standards.
However, the difference of the standard value is large concerning a return loss in every nationality. For this reason, one IC card-type modem could not correspond to the return loss standard of every nationality. Hereupon, the return loss means a relative attenuation volume of a signal level reflected to the side of the line, when the pseudo line of every nationality (a line simulator having a standard line characteristic) is connected to the line transformer within the IC card-type modem.
Fundamentally, the line transformer whose impedance is matched to the pseudo line should be designed for every nationality, in order to meet the return loss standard. For this reason, a single IC card-type modem which is in conformity with the line standard of each nationality has been demanded.
Besides, the specification of the switch connected to the IC card-type modem through the telephone line is different in every nationality. For this reason, an input output signal of the modem also had to correspond to the specification of every nationality. The input output signal of the modem is, for instance, a signal indicating a dial tone (a continuous tone when a receiver is picked up) to the switch and a busy tone.